There are people whose brain activity has ceased, who survived and still consider themselves to be the same person.
I guess it depends on how you define "ceased". As far as I understand, people who are in comas, or in shock, etc., still have a measurable level of brain activity (as well as metabolic activity, actually). When a person is cryonically frozen, however, all metabolic activity ceases (again, I could be wrong about this). This is rather a major difference. So, again, has anyone every successfully frozen and revived some complex mammal, such as a dog, and then verified that the dog still remembers all of its tricks after being revivied ? This would not prove that cryonics works on humans, of course, but it would be a pretty major piece of supporting evidence.
If you think living forever is worth money, it's reasonable to sign up for cryonics even if it's unlikely to work
I don't think this is true. For example, imagine that I told you I had a magic bean that, should you eat it, will cause you to be instantly revived after death, in perfect physical and mental health; and that I will sell you this bean for $1000. Would you buy the bean ?
Most reasonable people will answer "no", even though there's a non-zero probability that the bean is, indeed, magical. There are at least two reasons for this:
(edit: fixed formatting)
I guess it depends on how you define "ceased". As far as I understand, people who are in comas, or in shock, etc., still have a measurable level of brain activity (as well as metabolic activity, actually). When a person is cryonically frozen, however, all metabolic activity ceases (again, I could be wrong about this).
One of the papers referenced by Alcor in support of cryonics is this one. In this case, the patient seems to have been revived after having no electrical activity at all, which should demonstrate that the brain is not storing your personality of identity in any kind of "RAM".
From Mike Darwn's Chronopause, an essay titled "Would You Like Another Plate of This?", discussing people's attitudes to life:
Conclusion, graphs, and references in article. As usual, I recommend reading Chronopause.com as Darwin has many good articles; to quickly link a few: